The disclosure relates to a closure bolt for an injector of a modular common-rail fuel injection system.
Modular common-rail systems are characterized in that a part of the accumulator volume present in the system is provided in the injector itself. Modular common-rail systems are used in particularly large engines in which the individual injectors are, under some circumstances, mounted at considerable distances from one another. The mere use of a common rail for all of the injectors is not expedient in such engines because an extreme drop in injection pressure would occur during the injection owing to the long lines, such that the injection rate would drop significantly in the case of a relatively long injection duration. In such engines, therefore, provision is made for a high-pressure accumulator to be arranged in the interior of each injector. Such a design is referred to as a modular construction because each individual injector has its own high-pressure accumulator and can thus be inserted as an independent module. Here, a high-pressure accumulator is not to be understood to mean a conventional line, but is rather a pressure-tight vessel with an inlet line and an outlet line, the diameter of which vessel is considerably greater than that of the high-pressure lines in order that a certain injection flow rate can be discharged from the high-pressure accumulator without an immediate pressure drop occurring.
High-pressure fuel is supplied to injectors of modular common-rail systems from a high-pressure pump, wherein the supply is usually realized via an opening of the injector on the top side of the high-pressure accumulator (so-called “top feed”). The connection of the high-pressure line, which conducts the high-pressure fuel, to the injector is realized here by means of a closure bolt, the latter being provided with a high-pressure port and having a portion which can be inserted into the opening of the injector and which has a preferably conical sealing surface for closing the opening in a high-pressure tight manner. The volume of the integrated high-pressure accumulator is sealed off in this way. The closure bolt generally also has the function of conducting through the fuel for the adjacent injectors, for which purpose a second high-pressure port is provided.
A throughflow limiter is integrated into the closure bolt, which throughflow limiter separates the injector from the high-pressure fuel inflow in the event of an excessively high throughflow rate.
For manufacturing reasons, the closure bolt in the embodiment according to the prior art has a high-pressure bore which is continuous in an axial direction, into which high-pressure bore the high-pressure port issues radially and via which high-pressure bore the high-pressure fuel is conducted into the high-pressure accumulator. The axial high-pressure bore is sealed off to the outside by means of a closure screw.
A disadvantage of the described design of the closure bolt is that its inner contour is, owing to the geometry, subjected over the entire length to the full pressure of the high-pressure fuel, such that with regard to the geometric design and the roughness depths, high quality is required which is however difficult to achieve during production. Problems are posed in particular by the geometries, which are difficult to produce, for the throughflow limiter. This has the result that a durable design is no longer possible for system pressures of over 1600 bar.
It is therefore an aim of the present disclosure to avoid the above-described disadvantages. The disclosure is furthermore based on the object of providing a design which is simpler to produce and by means of which it is possible for the closing flow rate of the throughflow limiter to be adapted in a simple manner to the respective requirements.